1. Field of the Invention
This invention relates to tubing unloaders for production tubing in an oil well and, more particularly, to a novel tubing unloader in combination with a free point and a mechanical bumper sub that provides the operator with the capability to produce jarring forces on the production tubing in both the downward and upward directions.
2. The Prior Art
Production of crude oil from a completed, low pressure oil well is accomplished by inserting a production string into the well. The production string includes a bottom hole assembly consisting of a tail pipe with a gas buster, tubing anchor, seating nipple, and a rod pump. The rod pump is seated in the seating nipple. The rod pump is stroked by a mechanical rod known as a sucker rod which passes upwardly through the production tubing to a surface pump drive unit known as a "pump jack" or "horsehead pump" so named because of the shape of the lever arm of the pump drive unit. The production tubing carries the crude oil to the surface.
The tubing anchor is the bottom element of the production string and functions to releasably secure the bottom of the production tubing to the internal wall surface of the casing. The purpose of the tubing anchor is to allow for the application of tension on the production string. This tension is necessitated by the pumping action because the sucker rod reciprocates up and down inside the production tubing. On each upstroke an unanchored production tubing will move upwardly (breathing) as the fluid load inside the production tubing is transferred from the production tubing to the sucker rod. Further, the production tubing, for several joints above the rod pump, will be forcibly wrapped around the taut sucker rod string (buckling) causing excessive wear on the sucker rod and the production tubing with an accompanying increased friction drag along with a corresponding increase in the surface power requirements. These actions also severely reduce the effectiveness of the rod pump at each stroke and cause couplings in the production tubing to rub against the casing with resulting coupling wear. Ultimately, unless corrected, leakage occurs, or the production tubing and/or sucker rod will part resulting in substantial production losses.
From the foregoing, it is clear that the tubing anchor must be firmly set in the casing to assure that the production tubing is properly anchored. Once properly anchored, a predetermined tensile force is applied to the production tubing to preclude the foregoing breathing and buckling actions. Release of a conventional tubing anchor is customarily achieved by the application of a predetermined amount of set down weight coupled with a simultaneous rotation of the production tubing in the right hand direction. In the event normal release procedures fail, emergency shear release can be obtained by imposing a large, upwardly directed pull force against the production tubing.
A known problem of submersible pumps of this type is excessive wear due to sand and/or clogging from the sand and other debris that accumulates in the rod pump over time. A worn or stuck rod pump can result in a break in the sucker rod which will necessitate the sucker rod being fished and brought to the surface along with the rod pump. Desirably, the sucker rod would separate at or adjacent the rod pump. However, on many occasions the rod pump will not unseat out of the seating nipple. This condition is referred to as a stuck pump. Under this circumstance the sucker rod would be backed off and tripped out of the hole.
Customarily, the production tubing is filled with crude oil as a result of the pump stoppage occurring during operation. This condition is known as a "wet" production tubing. It is undesirable to pull a wet production tubing for several reasons. First, of course, a wet production tubing is extremely heavy requiring correspondingly heavy surface equipment to pull the production string. However, safety is probably the major reason why it is desirable to drain the production tubing prior to its being pulled from the oil well. Spilled crude oil resulting from pulling a wet production tubing represents a fire hazard and as well as a health and an environmental hazard.
One solution is to insert a tubing unloader in the production tubing one or two tubing lengths above the rod pump. One such device is shown in U.S. Pat. No. 4,903,326. This device incorporates externally located J-slots with shearable pins cooperating in the J-slots. The pins are designed to be sheared under emergency conditions. However, in the event the pins are sheared, a portion of the tubing unloader will be left in the well necessitating a major fishing job to retrieve the remainder of the tubing unloader, the lower tubing lengths, the rod pump, and the tubing anchor.
In view of the foregoing, it would be an advancement in the art to provide a tubing unloading apparatus and method whereby a wet production tubing can be readily and easily drained while at the same time incorporating in the tubing unloading apparatus a mechanism to enable the operator to selectively impart a downward jarring force as well as an upward jarring force on the tubing string. It would also be an advancement in the art to provide a tubing unloading tool having no shearing mechanism thereby effectively precluding the tool from being deliberately or even inadvertently sheared. Such a novel invention is disclosed and claimed herein.